Electrical tilt switches can operate to open or close electrical circuits as a function of the angle of inclination of the switch. Such switches normally include a free moving electrically conductive element that contacts at least two terminals when the conductive element moves to an operating position by gravity. A well-known form of the electrical tilt switch is the mercury switch. In a typical mercury switch, a glob of mercury moves freely within a sealed housing. As the housing is inclined, gravity pulls the glob of mercury to one end of the housing where it completes an electrical circuit. Mercury tilt switches are fairly easy to manufacture, however, due to environmental concerns, it is becoming increasingly difficult to manufacture any product that includes mercury because of its toxicity and disposal difficulty.
A common substitute for mercury in a tilt switch is free moving conductive element, such as a single metal ball. Tilt switches utilizing metal balls in place of globs of mercury are exemplified in U.S. Pat. No. 4,628,160 to Canevari and U.S. Pat. No. 3,763,484 to Byers. The use of a metal ball to complete an electric circuit is a simple and inexpensive way to create a tilt switch. Tilt switches have been used in connection with various applications, including electrical appliances to disconnect the power to the appliance where the appliance is accidentally tipped over. Tilt switches have also been used in connection with watt-hour meters to preserve the life of a battery in the unit during shipping, as exemplified in U.S. Pat. No. 5,107,203 to Timko, by disconnecting the battery when the meter is in the vertical (storage) position. A movable member (e.g., a metallic ball) within a tilt switch moves off of the internal contacts connecting the battery and the electronic circuitry when the meter is moved from the horizontal orientation.
The use of induction type watt-hour meters installed in meter sockets at customers' sites has led to wide-spread tampering of watt-hour meters in an effort to reduce the indicated consumption and thereby defraud the utility company through indication of less-than-actual power consumption. A large share of the meter tampering is done by residential and commercial customers with single-phase induction watt-hour meters. Of the more than twenty-five commonly detected methods of meter tampering, more than two-thirds of these require either removal of the meter from its socket or removal of the cover glass. One well-known method of meter tampering involves removal of the meter from its socket and reinstallation of the meter in an upside down position. Since the terminals are reversed and the meter registers are caused to run in reverse, thereby reducing the total indicated power consumption without interruption of the power supply to the user.
Although U.S. Pat. No. 4,039,943 to Tapscott and U.S. Pat. No. 4,542,337 to Rausch disclose watt-hour meters using a ball switch device to detect meter tampering, both use rather complex electromechanical devices to accomplish their goals. On one hand, Tapscott uses a gravity (ball) switch with an auxiliary magnet scheme to not only cause the meter to operate in the forward direction when installed upside down, but also to cause it to run at a greater rate than indicated by the actual power consumed, thereby penalizing the defrauder. Rausch, on the other hand, discloses an electromechanically complex hall switch having an enclosed race (circular track) with a plurality of spaced outer contacts, where a metallic ball moves around the enclosed race from one outer contact to another. Both devices are parts-intensive and costly to manufacture.
Accordingly, there is a need for a low-cost and highly reliable device that can be adapted to both new and existing meters to readily detect the most common types of meter tampering. A switching device or tilt sensor that addresses the aforementioned problems, as well as other related problems, is therefore desirable.